The present invention concerns advanced epoxy resins prepared by reacting an epoxy resin with a polyhydric phenolic compound wherein at least one of the reactants has a halogen atom which is meta with respect to a glycidyl ether group or a hydroxyl group.
Advanced epoxy resins containing halogen atoms are particularly useful in circuit boards or other electrical laminate applications, potting and encapsulation applications and other applications where flame retardant properties are desired. These halogen-containing advanced epoxy resins have the halogen atom in the ortho position with respect to the glycidyl ether groups. While these advanced halogen-containing epoxy resins possess the best properties to date which are particularly suitable for use in electrical laminates, potting and encapsulation applications and the like, it would be desirable if their properties were improved.
It has now been discovered that properties including one or more selected from thermal stability, glass transition temperature, melt viscosity to molecular weight relationship and resistance to forming hydrolyzed halides in the presence of a refluxing solution of an alkali metal hydroxide can be improved by employing an advanced epoxy resin wherein at least some of the halogen atoms are in the meta position with respect to a glycidyl ether group.